Heretofore, telephone lines have been primarily comprised of copper cables. In particular, pairs of copper cable have extended from telephone central offices to individual residential and commercial customers. Presently, there are on the order of one hundred fifty million telephone lines which extend to the premises of such customers ("subscribers"). The vast number of subscriber lines requires that means be provided for automatically testing such lines whereby, if a fault were to occur to a line, an appropriate service person could be dispatched to make repairs, possibly even before the subscriber becomes aware of the fault. Thus, automatic test equipment has been developed which is capable of testing subscriber lines repetitively and automatically.
As the metal network, comprised of copper cabling, is being replaced by fiber optic lines, the need has arisen to provide means for automatically testing the fiber optic communications lines, in much the same manner that the copper cables have heretofore been tested. A problem with the testing of fiber optic lines, however, is that, unlike copper, it is significantly more difficult to launch a test signal into a fiber optic path. In particular, it is quite simple with copper to make an electrical connection anywhere along the cable without otherwise impairing any other connection which has been made to the cable. With fiber optic lines, on the other hand, connections are significantly more difficult to make in that means must be provided for coupling the optical test signal onto the path to be tested in order to both launch the test signal into the line and to view the results of such test signal. In addition to the problem of coupling signals into a fiber optic line, there is also a problem in that the equipment which is used for such testing is extremely expensive. Consequently, the difficulty in coupling signals to a fiber optic line is compounded by the large expense involved in both coupling signals and in providing the signals in the first place. Thus, it would be desirable to be able to provide, and substantially reduce the expense of, means for automatically testing fiber optic lines which does not have the problems of the systems heretofore used.